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A temperature gradient chamber (TGC) is described which enables elevated CO2 concentrations and a dynamic temperature gradient to be imposed on field crops throughout their life cycle tinder standard husbandry. Air is circulated through two double-walled polyethylene-covered tunnels connected to a split heat pump system to give a near-linear temperature gradient along each tunnel. Solar energy gain along each tunnel and exchange with outer tunnel air flow contribute to the temperature gradient and also produce diurnal and seasonal temperature fluctuations corresponding to ambient conditions. Mean temperature gradients of between 3 and 5 °C have been recorded throughout the growing seasons of crops of lettuce, carrot, cauliflower and winter wheat. Elevated or present CO2 concentrations are maintained in each of two pairs of tunnels throughout the cropping season using pure CO2 injected through motorized needle valves. This system can realistically simulate aspects of the effects of projected future environmental change on crop growth, development and yield, and in particular the possible interaction of the effects of increased CO2 and temperature. [ABSTRACT FROM AUTHOR]

Field temperature gradient chambers designed for experiments on short-stature plants such as wheat are described. The chambers are portable, easily erected and dismantled, and are self-contained for control and measuring equipment The design is modular, the modules being bolted together longitudinally although separated by slotted transparent septa which divide the chamber into zones of different temperature. Fresh air, which is blown in horizontally into one end of the chamber by two fans and extracted by a fan mounted vertically at the other end, passes sequentially through the modules. The air stream progressively heats when the sun is shining. Fans are automatically speed-controlled in 100 steps between 20 and 100% of full output to keep the end-to-end temperature difference to within 5°C. During darkness, when the fans are running at minimum speed, heaters mounted in the outlet module are turned on. The chambers in the configuration described enclose 6 × 8m rows of crop, are 1.25 m high and have side walls which are entirely composed of rigid, vertically sliding doors for crop access. [ABSTRACT FROM AUTHOR]

The effect of temperature on short-term leaf extension rates was studies for two cool-season tusook grasses, Agropyron desertorum and Pseudoroegneria spicata, growing in the field under a variety of water stress and defoliation conditions. Leaf extension rates and air temperatures were monitored every half hour during numerous 12- to 65-h periods in three growing seasons using auxanometers constructed of precision resistors. For both species, a three-phase relationship between leaf extension rate and temperature was observed during diurnal cycles. Leaf extension rate increased linearly with temperature from dawn until midday (phase 1). Leaf extension then increased rapidly, reaching maximum rates in the early evening (approximately 1900h), despite decreasing temperatures during this period (Phase2). Finally, leaf extension rate declined with temperature from evening until dawn (Phase 3). This diurnal cycle was described by linear (Phase 1) and quadratic (Phases 2 and 3 combined) regression models. Although the rate of leaf extension and daily integrals were affected by the water stress and defoliation treatments, the diurnal pattern was consistently observed. Temperature was probably a major factor governing leaf extension rates at night (Phase 3), but it appeared unimportant in controlling leaf extension between dawn and midday. The relative importance of physiological and environmental factors controlling leaf extension rate appears to shift during the day in these species under filed conditions. [ABSTRACT FROM AUTHOR]

The productivity of the prickly-pear cactus Opuntia ficus-indica, which is cultivated worldwide for its fruits and stem segments, was predicted based on the responses of its net CO2 uptake to soil water status, air temperature and photosynthetic photon flux density (PPFD). Each of these environmental factors was represented by an index with a maximum value of unity when that factor was not limiting net CO2 uptake over a 24-h period. The water index, the temperature index, and the PPFD index were determined for 87 sites in the contiguous United States using data from 189 weather stations and for 148 sites worldwide using data from 1464 weather stations. The product of these three indices, the environmental productivity index (EPI), was used to predict the productivity of O. ficus-indica under current climatic conditions and under those accompanying a possible increase in the atmospheric CO2 level to 650 :μmol mol-1. Sites with temperatures always above -10°C and hence suitable for prickly-pear cultivation numbered 37 in the United States and 110 worldwide; such sites increased by 43 and 5%, respectively, for the global warming accompanying the elevated CO2. Productivity of O. ficus-indica was at least 15 tonnes dry weight hectare-1 year-1, comparable to that of many agronomic crops, for 20 sites with temperatures always above -10°C in the contigous United States and for 12 such sites worldwide under current climatic conditions; such sites increased by 85 and 117%, respectively, under the elevated CO2 condition, mainly because of direct effects of the atmospheric CO2 level on net CO2 uptake. In summary, simulations base on EPI indicate that O. ficus-indica may presently be advantageously cultivated over a substantial fraction of the earth's surface, such regions increasing markedly with a future doubling in atmospheric CO2 levels. [ABSTRACT FROM AUTHOR]

Abstract Two major components of climate change, increasing atmospheric [CO2 ] and increasing temperature, may substantially alter the effects of water availability to plants through effects on the rate of water loss from leaves. We examined the interactive effects of elevated [CO2 ] and temperature on seasonal patterns of stomatal conductance (g s ), transpiration (E ) and instantaneous transpiration efficiency (ITE) in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings. Seedlings were grown in sunlit chambers at either ambient CO2 (AC) or ambient + 180 µ mol mol-1 CO2 (EC), and at ambient temperature (AT) or ambient + 3·5 °C (ET) in a full-factorial design. Needle gas exchange at the target growth conditions was measured approximately monthly over 21 months. Across the study period and across temperature treatments, growth in elevated [CO2 ] decreased E by an average of 12% and increased ITE by an average of 46%. The absolute reduction of E associated with elevated [CO2 ] significantly increased with seasonal increases in the needle-to-air vapour pressure deficit (D ). Across CO2 treatments, growth in elevated temperature increased E an average of 37%, and did not affect ITE. Combined, growth in elevated [CO2 ] and elevated temperature increased E an average of 19% compared with the ACAT treatment. The CO2 supply and growth temperature did not significantly affect stomatal sensitivity to D or the relationship between g s and net photosynthetic rates. This study suggests that elevated [CO2 ] may not completely ameliorate the effect of elevated temperature on E , and that climate change may substantially alter needle-level water loss and water use efficiency of Douglas-fir seedlings. [ABSTRACT FROM AUTHOR]